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The [[Acasta Gneiss]] in the Canadian Shield in the [[Northwest Territories]], [[Canada]] is composed of the [[Archaean]] [[igneous]] and [[gneiss]]ic cores of ancient mountain chains that have been exposed in a [[glacier|glacial]] [[peneplain]]. Analyses of zircons from a felsic orthogneiss with presumed granitic protolith returned an age of 4.031 ± 0.003 Ga<ref name="Bowring"/>, which is the current oldest known terrestrial rock.
The [[Acasta Gneiss]] in the Canadian Shield in the [[Northwest Territories]], [[Canada]] is composed of the [[Archaean]] [[igneous]] and [[gneiss]]ic cores of ancient mountain chains that have been exposed in a [[glacier|glacial]] [[peneplain]]. Analyses of zircons from a felsic orthogneiss with presumed granitic protolith returned an age of 4.031 ± 0.003 Ga<ref name="Bowring"/>, which is the current oldest known terrestrial rock.


On September 25, 2008, researchers from [[McGill University]], [[Carnegie Institution for Science]] and [[UQAM]] announced that a rock formation, the [[Nuvvuagittuq]] [[greenstone belt]], exposed on the eastern shore of [[Hudson Bay]] in northern [[Quebec]] had a Sm-Nd age for extraction from the mantle of 4.28 billion years.<ref name="4.28">{{cite journal | doi = 10.1126/science.1161925 | year = 2008 | month = Sep | author = O'Neil, J; Carlson, Rw; Francis, D; Stevenson, Rk | title = Neodymium-142 evidence for Hadean mafic crust | volume = 321 | issue = 5897 | pages = 1828–31 | pmid = 18818357 | journal = Science (New York, N.Y.)}}</ref><ref name="McGill Greenstone Press release" >[http://www.mcgill.ca/newsroom/news/item/?item_id=102000 McGill University press release]</ref><ref name="MSNBC Oldest Rocks found" >[http://www.msnbc.msn.com/id/26890176/ Oldest rocks on Earth found]</ref><ref>http://www.sciencemag.org/cgi/reprint/321/5897/1828.pdf</ref> However, it is likely that the actual age of formation of this rock, as opposed to the extraction of its magma from the mantle, is likely closer to 3.8 billion years. <ref>[http://environment.newscientist.com/article/dn14818-discovery-of-worlds-oldest-rocks-challenged-.html Discovery of world's oldest rocks challenged]</ref>
On September 25, 2008, researchers from [[McGill University]], [[Carnegie Institution for Science]] and [[UQAM]] announced that a rock formation, the [[Nuvvuagittuq]] [[greenstone belt]], exposed on the eastern shore of [[Hudson Bay]] in northern [[Quebec]] had a Sm-Nd age for extraction from the mantle of 4.28 billion years.<ref name="4.28">{{cite journal | doi = 10.1126/science.1161925 | year = 2008 | month = Sep | author = O'Neil, J; Carlson, Rw; Francis, D; Stevenson, Rk | title = Neodymium-142 evidence for Hadean mafic crust | volume = 321 | issue = 5897 | pages = 1828–31 | pmid = 18818357 | journal = Science (New York, N.Y.)}}</ref><ref name="McGill Greenstone Press release" >[http://www.mcgill.ca/newsroom/news/item/?item_id=102000 McGill University press release]</ref><ref name="MSNBC Oldest Rocks found" >[http://www.msnbc.msn.com/id/26890176/ Oldest rocks on Earth found]</ref><ref>http://www.sciencemag.org/cgi/reprint/321/5897/1828.pdf</ref> However, it is argued that the actual age of formation of this rock, as opposed to the extraction of its magma from the mantle, is likely closer to 3.8 billion years. <ref>[http://environment.newscientist.com/article/dn14818-discovery-of-worlds-oldest-rocks-challenged-.html Discovery of world's oldest rocks challenged]</ref>


=== Recent research ===
=== Recent research ===

Revision as of 02:09, 23 March 2009

The oldest rock or rocks on Earth, as an aggregate of minerals that have not been subsequently melted or disaggregated by erosion, are from the Archean Eon. Such rocks are only exposed on the surface in very few places.[1]

There is some controversy about the oldest rocks based on the oldest dated mineral zircon. Some of the oldest surface rock can be found in the Canadian Shield, Australia, Africa and in other more specific places around the world. The ages of these felsic rocks are generally between 2.5 and 3.8 billion years. The approximate ages have a margin of error of millions of years. The oldest known rock on earth has been dated to 4.031 ± 0.003 billion years, and is part of the Acasta Gneiss of the Slave craton in northwestern Canada.[2]

Oldest rocks by category

Oldest terrestrial material

The oldest material of terrestrial origin that has been dated is a zircon mineral of 4,404 ± 8 Ma enclosed in a metamorphic gneiss in the Jack Hills of the Narryer Gneiss Terrane of Western Australia. The 4,404 ± 8 Ma zircon is a slight outlier, with the oldest consistently-dated zircon falling closer to 4.35 Ma.[3] This zircon is part of a population of zircons within the gneiss of greater than 3,900 Ma; the gneiss is considered to be no older than 3,800 Ma, which is the age of the youngest zircon in the rock.

Earth's oldest rock formation

The oldest rock formation is, depending on the latest research, either part of the Isua Greenstone Belt, Narryer Gneiss Terrane or the Acasta Gneiss. The difficulty in assigning the title to one particular block of gneiss is that the gneisses are all extremely deformed, and the oldest rock may be represented by only one streak of minerals in a mylonite, representing a layer of sediment or an old dyke. This may be difficult to find or map; hence the oldest dates yet resolved are as much generated by luck in sampling as by understanding the rocks themselves.

It is thus premature to claim that any of these rocks, or indeed that other formations of early Archaean gneisses, are the oldest formations or rocks on Earth; doubtless new analyses will continue to change our conceptions of the structure and nature of these ancient continental fragments.

Nevertheless, the oldest cratons on Earth include the Kaapvaal craton, the Western Gneiss Terrane of the Yilgarn craton (~2.9 - >3.2 Ga), the Pilbara Craton (~3.4 Ga), and portions of the Canadian Shield (~2.4 - >3.6 Ga). Parts of the poorly studied Dharwar craton in India are greater than 3.0 Ga. The oldest dated rocks of Baltic Shield are 3.5 Ga old [4].

Oldest rock on Earth

The Acasta Gneiss in the Canadian Shield in the Northwest Territories, Canada is composed of the Archaean igneous and gneissic cores of ancient mountain chains that have been exposed in a glacial peneplain. Analyses of zircons from a felsic orthogneiss with presumed granitic protolith returned an age of 4.031 ± 0.003 Ga[2], which is the current oldest known terrestrial rock.

On September 25, 2008, researchers from McGill University, Carnegie Institution for Science and UQAM announced that a rock formation, the Nuvvuagittuq greenstone belt, exposed on the eastern shore of Hudson Bay in northern Quebec had a Sm-Nd age for extraction from the mantle of 4.28 billion years.[5][6][7][8] However, it is argued that the actual age of formation of this rock, as opposed to the extraction of its magma from the mantle, is likely closer to 3.8 billion years. [9]

Recent research

The zircons from Jack Hills returned an age of 4.404 billion years, interpreted to be the age of crystallization. These zircons also show another interesting feature; their oxygen isotopic composition has been interpreted to indicate that more than 4.4 billion years ago there was already water on the surface of the Earth. The importance and accuracy of these interpretations is currently the subject of scientific debate. It may be that the oxygen isotopes, and other compositional features (the rare earth elements), record more recent hydrothermal alteration of the zircons rather than the composition of the magma at the time of their original crystallization.[citation needed]. In a paper published in the journal Earth and Planetary Science Letters, a team of scientists suggest that rocky continents and liquid water existed at least 4.3 billion years ago and were subjected to heavy weathering by an acrid climate. Using a ion microprobe to analyze isotope ratios of the element lithium in zircons from the Jack Hills in western Australia, and comparing these chemical fingerprints to lithium compositions in zircons from continental crust and primitive rocks similar to the Earth's mantle, they found evidence that the young planet already had the beginnings of continents, relatively cool temperatures and liquid water by the time the Australian zircons formed.[10]

See also

References

  1. ^ Some meteorites, such as the ALH84001 Mars meteorite found in Allan Hills Antarctica, are older but are not of terrestrial origin.
  2. ^ a b Bowring, Samuel A. (1999). "Priscoan (4.00-4.03 Ga) orthogneisses from northwestern Canada". Contributions to Mineralogy and Petrology. 134: 3. doi:10.1007/s004100050465.
  3. ^ Wilde SA, Valley JW, Peck WH and Graham CM (2001) Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature, v. 409, pp. 175-178. http://www.geology.wisc.edu/%7Evalley/zircons/Wilde2001Nature.pdf
  4. ^ Mutanen & Huhma (2003): The 3.5 Ga Siurua trondhjemite gneiss in the Archaean Pudasjärvi Granulite Belt, northern Finland Bulletin of the Geological Society of Finland,Vol. 75 (1–2) pp. 51–68
  5. ^ O'Neil, J; Carlson, Rw; Francis, D; Stevenson, Rk (2008). "Neodymium-142 evidence for Hadean mafic crust". Science (New York, N.Y.). 321 (5897): 1828–31. doi:10.1126/science.1161925. PMID 18818357. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  6. ^ McGill University press release
  7. ^ Oldest rocks on Earth found
  8. ^ http://www.sciencemag.org/cgi/reprint/321/5897/1828.pdf
  9. ^ Discovery of world's oldest rocks challenged
  10. ^ Newswise: Ancient Mineral Shows Early Earth Climate Tough on Continents Retrieved on June 15, 2008.
  • Zircons are Forever
  • "Western Australia's Jack Hills". NASA Earth Observatory newsroom. Retrieved 2006-04-28.
  • Bowring, S.A., and Williams, I.S., 1999. Priscoan (4.00-4.03 Ga) orthogneisses from northwestern Canada. Contributions to Mineralogy and Petrology, v. 134, 3-16.
  • Stern, R.A., Bleeker, W., 1998. Age of the world's oldest rocks refined using Canada's SHRIMP. the Acasta gneiss complex, Northwest Territories, Canada. Geoscience Canada, v. 25, p. 27-31
  • Yu A., Lee C-D and Halliday, A.N..Lutetium-Hafnium and Uranium-Lead Systematics of Early-Middle Archean Single Zircon Grains, Ninth Annual Goldschmidt Conference. 2
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